The DALI standard (“DALI” stands for Digital Addressable Lighting Interface”) was developed for modern lighting systems. This standard stipulates that a plurality of actuators, such as lighting units, light sensors and also emergency light units can be controlled from a central control via a DALI bus. The central control is connected to the DALI bus, in addition to command data, also a DC voltage with 9.5 Volts, or up to 22.5 Volts, which creates operating voltage for these actuators as they have no access to the AC voltage network, or are not supposed to be connected to it.
The DALI bus is thus an example of a databus which in the standby mode supplies voltage, in particular DC voltage.
In view of the fact that the DALI standard allows to connect up to 64 addressable actuators to the DALI bus, it is understood that one actuator can consume from the DALI bus a DC voltage for which the upper limit is 2 mA. The maximum allowable total current consumption is 250 mA. This still leaves room for some exceptions exceeding the upper limit.
The actuators which are still within the exception conditions are referred to as “DALI control devices”. Among these devices are signal generators such as light sensors which often must be installed in a location in which a connection to the AC power grid is not possible or difficult. This means that these signal generators can independently communicate with each other, and that they can also have the multi-master capability, which is to say that several active masters may be present in one bus system. Such “DALI control devices” are currently often designed as so called multi-sensors, which means that they possess a combined functionality of various sensors, such as for example that of a light sensor, a presence sensor, a motion sensor, a movement sensor and/or a sensor for an IR interface.
Emergency lights which according to prior art were not connected to AC current are not included in “DALI control devices”.
The task of emergency lights is to make sure that illumination will be still provided in case of a failure of the power supply for the participating actuators in the relevant space. That is why they are either provided for this purpose with a rechargeable device for storage of electrical energy, or they are connected to such a device. This device for storage of electrical energy is in the simplest case a capacitor, although most of the time it is a battery or a battery pack. The device for storage of electrical energy must be rechargeable again within 24 hours for normal operation of an emergency light, for example for a period of at least 3 hours. The current required for recharging the storage device with electrical energy was with emergency units according to prior art obtained with rectification from an AC power supply.
A corresponding connection to the AC power supply must be therefore provided for this purpose.